The present invention relates to a manual spray pump with variable volume, and more particularly a manual pump designed for spraying or dispensing a liquid fluid such as a perfume, a cosmetic, a pharmaceutical, or indeed a semi-liquid fluid such as a cream.
For example, French patents Nos. 1 486 392 (Rudolph Albert) and 2 305 241 (Societe Technique de Pulverisation--S.T.E.P.) disclose such pumps, each comprising a cylindrical pump body in which there slides a hollow piston provided with an outlet channel. The pump body and the piston define a pump chamber that normally contains the fluid to be sprayed or dispensed, and that communicates with a fluid tank via an inlet orifice. In addition, a valve rod disposed in the pump chamber is urged by a spring towards a valve seat formed on the piston, thereby closing the outlet channel and urging the piston towards a rest position in which the volume of the pump chamber is at a maximum. The valve rod is secured to a differential piston capable of sliding on or in an internal cylindrical portion of the pump body which is in communication with the fluid tank via the inlet orifice.
When the piston is actuated against the urging of the spring, the differential piston closes communication between the pump chamber and the fluid tank, either by means of an inlet non-return valve integrated in the differential piston, or else by means of the differential piston engaging in or on the inside cylindrical portion of the pump body. Actuation of the piston tends to reduce the volume of the pump chamber, thereby increasing the pressure in the pump chamber: the increased pressure acts on the differential piston to move the piston away against the urging of the spring, thereby opening the outlet channel of the piston through the valve rod, and thus causing a volume of fluid contained in the pump chamber to be expelled via the outlet channel as the piston moves in the pump body.
When the piston is no longer actuated, the spring urges the valve rod back towards the piston, thereby closing the outlet channel, after which it urges the piston back to its rest position. During this movement, the volume of the pump chamber increases, such that suction is established in the pump chamber. When the differential piston includes an inlet valve, the suction opens the inlet valve and causes the fluid to be admitted into the pump chamber from the beginning of the return movement of the piston. Otherwise, i.e. if communication between the pump chamber and the tank is interrupted by engagement of the differential piston on or in the cylindrical inside portion of the pump body, then the fluid enters the pump chamber only after the piston has returned to its rest position, in which the engagement has ceased.
In prior art pumps of the general type described above, the volume of delivered fluid is fixed. This volume depends on two parameters, namely the section of the pump chamber and the stroke of the piston: the section of the pump chamber is naturally unalterable, and in prior art pumps the stroke of the piston is determined by a top abutment and by a bottom abutment that are secured to the pump body and that are therefore fixed.
This can be a drawback, for example when the pump contains a pharmaceutical: with a conventional pump, there is no way of varying the dose that is delivered, e.g. as a function of the condition or the age of the patient. Also, with conventional pumps, two pumps that deliver different volumes necessarily include parts that are different and, assuming that the parts are made of molded plastics material, thus requiring some of the manufacturing molds to be different. The pump manufacturer is thus obliged to have additional molds, and molds are known to be very expensive.
An object of the present invention is to avoid those drawbacks by providing a variable volume pump.
It is known from document FR-1 101 114 that the stroke of the piston can be varied by means of a screwable ferrule that acts as the bottom abutment. By screwing in the ferrule to a greater or lesser extent, the volume of fluid that is delivered can be influenced. However, the ferrule constitutes an additional element in the pump. Like all the other components of the pump, that element must be molded and assembled. Molding requires a distinct mold to be made, and assembly requires a machine capable of taking hold of the element, orienting it properly, and then inserting it. In addition, since in is an element with a screw thread, the part which receives it must also have a thread. That all contributes to increasing the cost of the pump.